Power converter

1. A layered DC busbar structure comprising: a positive DC substrate arranged to carry a positive DC voltage, said positive DC substrate being arranged on a first layer; a negative DC substrate arranged to carry a negative DC voltage, said negative DC substrate being arranged on a second layer; a DC neutral substrate arranged on a central layer between said first and second layers; and an AC substrate arranged to carry an AC voltage, said AC substrate being arranged on the central layer and substantially coplanar with the DC neutral substrate.

2. The layered DC busbar structure as claimed in claim 1 , further comprising a plurality of AC substrates, each arranged to carry a respective AC voltage, wherein each AC substrate is arranged on the central layer and substantially coplanar with the DC neutral substrate.

3. The layered DC busbar structure as claimed in claim 1 , wherein the positive and negative DC substrates substantially fully cover the central layer.

4. The layered DC busbar structure as claimed in claim 1 , further comprising a plurality of vias that provide electrical connections between the substrates and the rails and nodes of an external power converter.

5. The layered DC busbar structure as claimed in claim 1 , further comprising vias to provide for electrical connections to an external drive circuit.

6. A power converter comprising a DC link, wherein the DC link comprises a layered DC busbar structure as claimed in claim 1 .

7. The power converter as claimed in claim 6 , further comprising: a DC voltage supply connected between a positive DC supply rail and a negative DC supply rail, wherein the positive DC supply rail is connected to the positive DC substrate, and wherein the negative DC supply rail is connected to the negative DC substrate; a first capacitor and a second capacitor connected in series between said positive and negative DC supply rails, said first and second capacitors being connected at a first node therebetween, wherein the first node is connected to the DC neutral substrate; an internal branch module comprising a first switching arrangement connected between the first node and a second node, wherein the second node is connected to the AC substrate; and an external branch module comprising a second switching arrangement, said second switching arrangement comprising first and second switches connected in series at the second node.

8. The power converter as claimed in claim 7 , wherein the power converter comprises an external AC circuit is connected to the second node, optionally wherein the external circuit comprises an inductor connected to the second node.

9. The power converter as claimed in claim 7 , wherein the first and second capacitors are mounted directly on the layered substrates.

10. The power converter as claimed in claim 7 , further comprising a second external branch module comprising a third switching arrangement, said second switching arrangement comprising first and second switches connected in series at the second node, optionally wherein the external branch modules are placed side by side.

11. The power converter as claimed in claim 7 , wherein the internal branch module comprises first and second elongate substrates aligned along a first axis, said first elongate substrate being connected to the first node and said second elongate substrate being connected to the second node.

12. The power converter as claimed in claim 7 , wherein the external branch module comprises first, second, and third elongate substrates aligned along a second axis, wherein the first elongate substrate is connected to the positive DC supply rail, the second elongate substrate is connected to the negative DC supply rail, and the third elongate substrate is connected to the second node.

13. The power converter as claimed in claim 6 , further comprising a heat sink and a further layered DC busbar, wherein the first layered DC busbar is positioned on a first side of the heat sink and the second DC busbar is positioned on a second side of the heat sink, opposite to said first side.